Team:Thessaly/Hardware
Overview
Being a two-phase project comes with a lot of changes along the way, one of which being the hardware side
of the project. Last year we tackled the problem by dividing our design into individual parts and
analyzing their behavior and purpose within our device. This year we built upon the knowledge of our last year’s attempts
and approached the problem holistically. We tried to fit everything correctly into the capsule to make a prototype whilst testing new approaches in order to improve our design.
Introduction
At the beginning of this year, we chose to take a different approach in relation to the one we followed during the first phase of our project. We set our goals to make our
project more broad and more holistic, concluding on manufacturing a medical kit.
So now our project was divided in three. One of the thirds is the capsule.
The reason we decided to design the capsule in the first year was because we saw a gap in the market for such a capsule- but we will talk about that in the next section- and we also saw a gap in the gut microbiome research. Now the reason we wanted this year to redesign the capsule, was to, firstly, create a more holistic design and secondly to improve the -pun intended- capsule and to correct our mistakes from last year and make many more this year through the design, build, test, learn cycle.
The reason we decided to design the capsule in the first year was because we saw a gap in the market for such a capsule- but we will talk about that in the next section- and we also saw a gap in the gut microbiome research. Now the reason we wanted this year to redesign the capsule, was to, firstly, create a more holistic design and secondly to improve the -pun intended- capsule and to correct our mistakes from last year and make many more this year through the design, build, test, learn cycle.
Design
At the beginning of the team formation and whilst the dry lab sub team was getting informed on
last year's project, we got debriefed on last year's design and how the dry lab sub team worked.
Their approach was to analyze each part to a good degree, but independently from the whole system.
That approach obviously has some advantages, like not having to worry about compatibility with the
rest of the system or about the time that it will take or the complexity. However, that approach
lacks the holistic approach that systems need to be completed and work how they are supposed to.
Therefore, after we got up to speed with everything concerning the project’s progress and after
we decided as a team our goal for the project, we started. Our initial goal was to take the
components from last year’s project and make them work in a harmonious way.
Figure 1: The design of the capsule from the first phase of the project
As you can see from the above image there are a lot of parts in this tiny capsule.
Although they seem like they are working together nicely, they are not in reality
unfortunately. So, our job throughout 2021 was to make them work.
Components
Last year’s part list
Microcontroller |
PCB |
Battery (silver oxide button battery) |
PDMS (silicone-based coating) |
RF transceiver |
Kill switch |
Parylene-C membrane |
Electrodes |
Semipermeable membrane |
In the process of experimenting with the old parts of the system we struggled to make them work as we wanted them to. Some parts were undefined, some parts did not fit properly, and some parts were outright not in line with the new goals of the projects. Thus, we began part by part replacing them, based on the various criteria we had set, in order for the capsule to work properly. After many iterations and mistakes, we had our first abstract design of the capsule.
Figure 2: This year’s abstract capsule design,
showcasing the initial spatial arrangement
This year’s part list
This year we shrunk down our part list and changed a few of them, so they can be in-line with our new
requirements. Let’s analyze our design choices, starting by the processor.
Last year we designed the antenna and processor to be independent from each other, while this year we fused them into one. Our choice for the central processing unit of our system is the Cortex M0+ microprocessor that is part of the DA14531 SOC. This System-On-a-Chip (SOC) not only is incredibly small and versatile, but it also solves the need for an independent antenna, since it provides it on board.
Another reason we chose the Smartbond SOC is because of the antenna that it provides, which transmits in the bandwidth of 2.4 GHz, which coalesces with the Bluetooth protocol. We will utilize these Bluetooth capabilities, as we have designed a mobile phone application to communicate with the capsule.
Moving on, the next component to consider is the batteries. We chose three batteries instead of two in our initial design, because there was extra space in our new capsule design, which we will utilize to improve its battery life. The battery we will use is the same from last year’s design, but a model smaller in size, the MAXELL 371 SR920SW.
For the next component, we have the outer cell of the capsule, which is made from Polydimethylsiloxane or PDMS. PDMS belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. These types of compounds are commonly used in medical applications, such as contact lenses and most importantly they are used in capsules (Mimee et al., 2018). Thus, our choice for the outer layer of our capsule was both backed by research and existing products (Min et al., 2020).
Continuing down the parts list, we have the mechanical kill switch. The purpose of the mechanical kill switch is to neutralize the live bacteria in the case of the capsule breaking under a certain amount of pressure. We use this mechanical kill switch as an additional failsafe to our biological auxotrophy kill switch.
A Parylene-C membrane will be used in our system here, its main purpose being the insulation of the electronic circuit from moisture and chemicals found in the gut.
Our next component is one of utter importance, the electrochemical sensor. This sensor registers the signal produced by our whole-cell biosensor, thus the SCFA levels, and transmits the data to the processor. Our design has 3 electrodes, a gold standard electrode, a platinum as the counter electrode and a silver chloride electrode as the reference electrode
Our last component is the semipermeable membrane, which is theoretical, as we found out through Integrated Human Practices interviews with professors specializing in this field. The reason they gave is, firstly such membrane does not exist in the market and secondly the reason it does not exist is because of how specialized it is. It is characterized as specialized because SCFA molecules are intricate and significantly smaller than Tyrosinase, which we also want to block from entering the system.
In terms of spatial arrangement of the capsule’s components, we took inspiration from papers concerning capsule endoscopy (Zhao et al., 2015) and tried to implement it into our needs.
We began our design process with the bottom-up philosophy in mind. The first step in the process was to gather all the dimensions of the selected parts and then create rough sketches of how they would fit in our capsule, which already had some constraints regarding dimensions, based on other capsule dimensions (Zhao et al., 2015) we have found in scientific articles. The dimensions are the following: 22 mm x 11mm x 11mm.
These dimensions were decided based on safety, as the smaller the capsule, the less likely is the capsule will get stuck inside the alimentary canal (Zhuang et al., 2011). Keeping that in mind, we tried to fit everything and make them work properly. Thankfully for us we found exactly what we were looking for, that being one of the smallest SoC in the world, small batteries, and small sensing electrodes. Our design mimics the design of endoscopy capsules, as we put everything parallel to the shape of the capsule to try to maximize the space available to us.
In Figure 3 we can see the first designs with the original dimensions and besides them we can see some
of the components of the capsule. As we researched more and experimented with the dimensions and the
parts, we came to the realization that with the original dimensions of 22 mm x 11mm x 11mm we had more
space than we needed.
As we can see in Figure 4, with the original capsule size, there was plenty of space to spare, which led us to the addition of the third battery and then consequently reduce the capsule size down to 15mm of length
Finally, we added the mechanical kill switch to the capsule model. Essentially, the kill switch is a reservoir that holds L-arabinose inside it.
In Figure 6 we can see the placement and the design of the mechanical kill switch. The system works with pressure as its activator. We carefully designed the reservoir with the funnel facing downwards in order to direct the fluid directly to the bacteria and not let them flop around first. More specifically, the membrane that keeps the fluid in the reservoir will break above a certain Pa value and release all the fluid and deactivate or “kill” the bacteria as to not inflict any damage to the human or animal gut. That value represents the breaking point of the capsule or at least close to it so that we can be certain it will break under the correct conditions and be in line with our safety protocols. However, this value needs to be experimentally determined.
In Figure 7, we can see the final design of the capsule, with original dimensions. We used this model in 3D-printer to bring the capsule into life and really understand the scale and detect any mistakes.
SOC DA14531 |
3 Batteries (silver oxide button battery) |
PDMS (silicone-based coating) |
Kill switch (tank with L-arabinose) |
Parylene-C membrane |
3 tiny electrodes |
Semipermeable membrane |
Last year we designed the antenna and processor to be independent from each other, while this year we fused them into one. Our choice for the central processing unit of our system is the Cortex M0+ microprocessor that is part of the DA14531 SOC. This System-On-a-Chip (SOC) not only is incredibly small and versatile, but it also solves the need for an independent antenna, since it provides it on board.
Another reason we chose the Smartbond SOC is because of the antenna that it provides, which transmits in the bandwidth of 2.4 GHz, which coalesces with the Bluetooth protocol. We will utilize these Bluetooth capabilities, as we have designed a mobile phone application to communicate with the capsule.
Moving on, the next component to consider is the batteries. We chose three batteries instead of two in our initial design, because there was extra space in our new capsule design, which we will utilize to improve its battery life. The battery we will use is the same from last year’s design, but a model smaller in size, the MAXELL 371 SR920SW.
For the next component, we have the outer cell of the capsule, which is made from Polydimethylsiloxane or PDMS. PDMS belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. These types of compounds are commonly used in medical applications, such as contact lenses and most importantly they are used in capsules (Mimee et al., 2018). Thus, our choice for the outer layer of our capsule was both backed by research and existing products (Min et al., 2020).
Continuing down the parts list, we have the mechanical kill switch. The purpose of the mechanical kill switch is to neutralize the live bacteria in the case of the capsule breaking under a certain amount of pressure. We use this mechanical kill switch as an additional failsafe to our biological auxotrophy kill switch.
A Parylene-C membrane will be used in our system here, its main purpose being the insulation of the electronic circuit from moisture and chemicals found in the gut.
Our next component is one of utter importance, the electrochemical sensor. This sensor registers the signal produced by our whole-cell biosensor, thus the SCFA levels, and transmits the data to the processor. Our design has 3 electrodes, a gold standard electrode, a platinum as the counter electrode and a silver chloride electrode as the reference electrode
Our last component is the semipermeable membrane, which is theoretical, as we found out through Integrated Human Practices interviews with professors specializing in this field. The reason they gave is, firstly such membrane does not exist in the market and secondly the reason it does not exist is because of how specialized it is. It is characterized as specialized because SCFA molecules are intricate and significantly smaller than Tyrosinase, which we also want to block from entering the system.
Capsule design
In terms of spatial arrangement of the capsule’s components, we took inspiration from papers concerning capsule endoscopy (Zhao et al., 2015) and tried to implement it into our needs.
We began our design process with the bottom-up philosophy in mind. The first step in the process was to gather all the dimensions of the selected parts and then create rough sketches of how they would fit in our capsule, which already had some constraints regarding dimensions, based on other capsule dimensions (Zhao et al., 2015) we have found in scientific articles. The dimensions are the following: 22 mm x 11mm x 11mm.
These dimensions were decided based on safety, as the smaller the capsule, the less likely is the capsule will get stuck inside the alimentary canal (Zhuang et al., 2011). Keeping that in mind, we tried to fit everything and make them work properly. Thankfully for us we found exactly what we were looking for, that being one of the smallest SoC in the world, small batteries, and small sensing electrodes. Our design mimics the design of endoscopy capsules, as we put everything parallel to the shape of the capsule to try to maximize the space available to us.
Figure 3: Draft 3d models of the capsule and
its components
Figure 4: Capsule bisected in half to show the components.
As we can see in Figure 4, with the original capsule size, there was plenty of space to spare, which led us to the addition of the third battery and then consequently reduce the capsule size down to 15mm of length
Figure 5: Capsule bisected in half to illustrate the space available and the number of batteries
Finally, we added the mechanical kill switch to the capsule model. Essentially, the kill switch is a reservoir that holds L-arabinose inside it.
Figure 6: Front view of the capsule, highlighting
the L-arabinose reservoir or “kill switch”
In Figure 6 we can see the placement and the design of the mechanical kill switch. The system works with pressure as its activator. We carefully designed the reservoir with the funnel facing downwards in order to direct the fluid directly to the bacteria and not let them flop around first. More specifically, the membrane that keeps the fluid in the reservoir will break above a certain Pa value and release all the fluid and deactivate or “kill” the bacteria as to not inflict any damage to the human or animal gut. That value represents the breaking point of the capsule or at least close to it so that we can be certain it will break under the correct conditions and be in line with our safety protocols. However, this value needs to be experimentally determined.
Figure 7: Pictured here is the final outer cell of our capsule
In Figure 7, we can see the final design of the capsule, with original dimensions. We used this model in 3D-printer to bring the capsule into life and really understand the scale and detect any mistakes.
Figure 8: Our 3D printed capsule
Mechatronic Design
